Voltage regulators



Sept. 27, 1966 D. s. ADAMS VOLTAGE REGULATORS Filed April 5, 1963 L AD United States Patent 3,275,924 VOLTAGE REGULATORS Derek Stanley Adams, Acocks Green, Birmingham, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England FiledApr. 5, 1963, Ser. No. 270,963 Claims priority, application Great Britain, Apr. 11, 1962, 13,942/ 62 7 Claims. (Cl. 322-28) The object of this invention is to provide a voltage regulator in a convenient form.

A voltage regulator in accordance with the invention comprises in combination first and second terminals for connection to a DC. output from a generator the output of which is to be controlled, a first transistor having its emitter connected to the first terminal through a resistor, and to the second terminal through a Zener diode, and its base connected to the first terminal through a diode, a second transistor of opposite conductivity type to the first transistor and having its emitter connected through a field Winding of the generator to the second terminal, its base connected to the collector of the first transistor and its collector connected to the first terminal through the diode, and a resistive path through which the collector of the second transistor is connected to the second terminal, the arrangement being such that when the output voltage of the generator exceeds a predetermined value, the Zener diode becomes conductive, and current flow in the field winding is reduced.

The resistive path may be provided by a resistor connected between the collector of the second transistor and the second terminal. Alternatively, the characteristics of the second transistor may be such that the leakage through it when in the off condition provides the required resistive path.

In the accompanying drawings FIGURE 1 is a circuit diagram illustrating one example of the invention, and FIGURES 2 and 3 respectively illustrate suitable forms of semi-conductor crystals constituting portions of the circuit.

Referring to FIGURE 1, there is provided positive and negative terminals 6, 7 for connection to the DC. output of a generator 8 which supplies a load 9 in the form of a battery. The terminals 6, 7 are interconnected through parallel paths one of which contains a diode 10 and a resistor 11 in series and the other of which includes resistors 12, 13, 14 in series. There is further provided a transistor 15 of the p-n-p type having its emitter connected to the terminal 6 through a resistor 16, and to a variable point on the resistor 13 through a Zener diode 17. The base of the transistor 15- is connected to the terminal 6 through the diode 10, whilst its collector is connected to the base of a transistor 18 of the n-p-n type. The transistor 18 has its collector connected through the diode 10 to the terminal 6, and its emitter connected to the terminal 7 through a field winding 19 of the generator 8.

The operation of the circuit is as follows: when the voltage across the terminals 6, 7 is low, the diode 10 and the resistor 11 act as a potential divider to maintain the collector voltage of the transistor 18 negative with respect to the emitter voltage of the transistor 15. This permits conduction of the transistor 15, the current flow through which serves to hold the transistor 18 on so that current flows in the winding 19.

When the voltage across the terminals 6, 7 rises, the voltages across the resistor 16 and the diode 10 also rise, the known characteristics of the diode being such that when a substantial current is flowing through it it acts as a substantially constant and relatively small resistance. The transistors 15, 18 are thus maintained conductive as the voltage rises. However, when a predetermined voltage is reached, the Zener diode 17 breaks down, and thereafter the emitter voltage of the transistor 15 is held constant. However, the collector voltage of the transistor 18 continues to rise with the result that the transistor 15 is switched off, with consequential switching off of the transistor 18. The change from the conductive to the non-conductive state is rapid due to the positive feedback between the transistors.

The purpose of using a diode in place of a resistor is as follows. If a resistor were used, when the transistor 18 was switched off, its collector voltage would be increased substantially. However, when the transistor 18 is switched oif, the current flowing through the diode falls and the diode then operates on the position of its voltagecurrent curve at which the resistance of the diode is relatively high. Thus, the collector voltage will not be so much as if a resistor were used having a constant resistance equal to the substantially constant resistance of the diode when a substantial current is flowing through it. The diode thus serves to provide the positive feedback which is required for rapid switching whilst maintaining the change in collector voltage of the transistor 18 reasonably small. It will be understood that this is important, since the voltage at which the transistors became conductive differs from the voltage at which they became nonconductive by a voltage dependent on the aforesaid change in collector voltage, which must therefore be maintained as low as possible.

The transistors 15, 18 can be combined in a single crystal as shown in FIGURE 2. The crystal includes nlayers 21, 22 separated by a p-layer 23, the layer 21 incorporating a further p-layer 24. The emitter, base and collector of the transistor 18 are constituted by the layers 22, 23, 21 respectively, whilst the emitter, base and collector of the transistor 15 are constituted by the layers 24, 21, 23 respectively.

Although a separate diode can be employed, it is preferred to combine the diode with the crystal. For this purpose an extra p-type layer 25 is formed on the layer 21, the diode being constituted by the layers 25, 21.

The resistance chain 12, 13, 14 permits adjustment of the voltage at which regulation commences. Moreover, by utilizing as one of the resistors 12, 14 a device the resistance of which is particularly sensitive to temperature, an automatic temperature compensation can be obtained.

It will be understood that it is essential that a resistive path is provided through the diode 10 to the terminal 7 when the transistor 18 is cut off. However, provided that the leakage current of the transistor 18 is high enough to provide the required resistive path, the resistor 11 can be omitted.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A voltage regulator for use with a DC. generator having a field winding, comprising in combination first and second terminals for connection to said generator, at first transistor, a resistor through which the emitter of the first transistor is connected to the first terminal, a Zener diode through which the emitter of the first transistor is connected to the second terminal, a diode through which the base of the first transistor is connected to the first terminal, a second transistor of opposite conductivity type to the first transistor and having its emitter connected through said field winding of the generator to the second terminal, its base connected to the collector of the first transistor and its collector connected to the base of said first transistor, and a resistive path through which the collector of the second transistor is connected to the second terminal, said Zener diode becoming conductive when the output voltage of the generator exceeds a predetermined value and said second transistor switching between on and off states to regulate the output voltage of the generator.

2. A voltage regulator as claimed in claim 1 in which the resistive path is provided by connecting a resistor between the collector of the second transistor and the second terminal.

3. A voltage regulator as claimed in claim 1 in which the resistive path is provided by the leakage path through the second transistor when the second transistor is cut off.

4. A voltage regulator as claimed is claim 1 in which said transistors are constituted by a single semi-conductor crystal.

5. A voltage regulator as claimed in claim 1 in which said transistors and the diode are constituted by a single semi-conductor crystal.

6. A voltage regulator as claimed in claim 1 including a resistance chain connected between the first and second terminals, the Zener diode being connected between the emitter of the first transistor and a variable point on the resistance chain.

7. A voltage regulator as claimed in claim 6 in which the resistance chain includes a resistor for compensating automatically for temperature changes.

References Cited by the Examiner OTHER REFERENCES I.B.M. Technical Disclosure Bulletin, vol. 4, No. 9, February 1962, Transistor Regulators, Ferrailo & Gass, pages 41 and 42.

20 MILTON O. HIRSHFIELD, Primary Examiner.

I. J. SWARTZ, Assistant Examiner. 

1. A VOLTAGE REGULATOR FOR USE WITH A D.C. GENERATOR HAVING A FIELD WINDING, COMPRISING IN COMBINATION FIRST AND SECOND TERMINALS FOR CONNECTION TO SAID GENERATOR, A FIRST TRANSISTOR, A RESISTOR THROUGH WHICH THE EMITTER OF THE FIRST TRANSISTOR IS CONNECTED TO THE FIRST TERMINAL, A ZENER DIODE THROUGH WHICH THE EMITTER OF THE FIRST TRANSISTOR IS CONNECTED TO THE SECOND TERMIANL, A DIODE THROUGH WHICH THE BASE OF THE FIRST TRANSISTOR IS CONNECTED TO THE FIRST TERMINAL A SECOND TRANSISTOR OF OPPOSITE CONDUCTIVITY TYPE TO THE FIRST TRANSISTOR AND HAVING ITS EMITTER CONNECTED THROUGH SAID FIELD WINDING OF THE GENERATOR TO THE SECOND TERMINAL, ITS BASE CONNECTED TO THE COLLECTOR OF THE FIRST TRANSISTOR AND ITS COLLECTOR CONNECTED TO THE BASE OF SAID FIRST TRANSISTOR, AND A RESISTIVE PATH THROUGH WHICH THE COLLECTOR OF THE SECOND TRANSISTOR IS CONNECTED TO THE SECOND TERMINAL, SAID ZENER DIODE BECOMING CONDUCTIVE WHEN THE OUTPUT VOLTAGE OF THE GENERATOR EXCEEDS A PREDETERMINED VALUE AND SAID SECOND TRANSISTOR SWITCHING BETWEEN ON AND OFF STATES TO REGULATE THE OUTPUT VOLTAGE OF THE GENERATOR. 